Description: (Applicant s Description) The long term objective of this application is to determine whether Bowman-Birk inhibitor (BBI) in Concentrate (C), a protease inhibitor extracted from soybeans, can cause regression of oral leukoplakia (OL) and whether certain candidate intermediate marker endpoints can predict response by serving as a surrogate for oral leukoplakia. The ultimate goal of this research is to prevent human cancer. The specific aims are: (1) To conduct a short-term (one-month) phase IIa cancer control chemoprevention trial of BBIC in patients with OL. The purposes of this trial are: a. To determine the effects of BBIC on the oral cavity. b. To measure the response of IME to BBIC. c. To determine the dose of BBIC at which the IME are not further lowered. (2) To conduct a placebo-controlled and randomized long-term phase IIb cancer control chemoprevention trial of BBIC inpatients with OL. Using the dose of BBIC determined in the IIa trial the essential features include: a. To determine the clinical and histologic response rate of OL to BBIC. b. To serially measure the effect of BBIC on IME levels. c. To correlate the clinical and histologic responses of OL to the effect on protease activity levels and levels of c-erb-B and c-fos expression. d. To determine the individual and group side-effects to BBIC